Approximate time for coarse constituents? (8)

I believe the answer is:

roughage

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'for coarse constituents?' is the definition.
I can't judge whether this defines the answer.

'approximate time' is the wordplay.
'approximate' becomes 'rough' (I've seen this in another clue).
'time' becomes 'age' (an age is a period of time).
'rough'+'age'='ROUGHAGE'

Can you help me to learn more?

(Other definitions for roughage that I've seen before include "Indigestible fibre" , "Indigestible material good for intestines" , "It aids digestion" , "Bulk" , "Indigestible material to stimulate intenstines" .)

I've seen this clue in the Sydney Morning Herald.

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